Field of the Invention:
The present invention relates generally to sealing gaskets and sealing systems used for pipe joints in plastic pipelines, such as municipal water and sewer lines, in which a male spigot pipe section is installed within a mating female socket pipe section to form a pipe joint.
Description of the Prior Art:
Fluid sealing systems for plastic, fluid conveying pipes are used in a variety of industries. The pipes used in such systems are typically formed from thermoplastic materials including polyolefins and PVC. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a raceway or groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. Various types of sealing technologies have been employed to assure the sealing integrity of the pipe joint. It is important that the sealing gasket not be dislodged during the joint make up and that the gasket not become twisted or otherwise compromised in field applications. It is also important that the gasket not extrude out of the pipe groove under various pressure conditions.
Earlier gasketed sealing systems are known in which a homogeneous rubber gasket was generally deformable, allowing it to be flexed or bent by hand, accepting inverse curvature, and inserted within a mating internal raceway formed in the female, belled pipe end. The raceway in the female pipe bell end was pre-formed using a collapsible mandrel belling tool at the pipe manufacturing facility. Due to the elastic nature of rubber these gaskets will extrude through the annular space created by the male pipe spigot end and female lip of the bell under cyclic and high pressure conditions. These gaskets also proved to be relatively easy to displace during field assembly of the joint. A prior art attempt to prevent gasket extrusion of such pipe joints involved the use of a pipe gasket having a first distinct body region formed of an elastically yieldable sealing material, such as rubber, bonded to a second distinct body region formed of a more rigid material, such as a rigid plastic. The intent was that the rigid body region of the gasket would assist in holding the gasket in place within the pipe groove. Other approaches to the problem included the use of a homogeneous rubber ring with a discrete stiffening band which was inserted into a groove provided on the internal diameter of the rubber ring. In the other prior art systems, a homogeneous rubber gasket body was bonded with an internal or external metal, or plastic, reinforcing band or an internal metal band or ring. Each of these solutions had critical limitations. For example, the internal metal reinforcing band must be treated properly for metal bonding, coated to prevent rusting, and situated precisely inside the mold using a series of pins. The prior art plastic/rubber composites sometimes allowed the infiltration of dirt and debris between the bell raceway and the outer diameter of the gasket. The plastic region in some cases, reduced the rubber surface contact area, sometimes leading to problems in providing the needed sealing in all conditions, including high pressure, low pressure and cyclic surges. Compatible materials were necessary when bonding the homogeneous rubber gasket body with the plastic reinforcing band. Poor bonding resulted in separation of the two elements. The reinforcing band was subject to being misplaced and breakage in the two part system. Thus, in some cases, the prior art solutions failed to provide the needed joint integrity, often contributing to the complexity and expense of the manufacturing operation and field installation.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system employed a combined mould element and sealing ring for sealing a joint between the socket end and spigot end of two cooperating pipes formed from thermoplastic materials. In the Rieber process, an elastomeric gasket was installed within an internal raceway or groove in the socket end of the female pipe as the female or belled end was simultaneously being formed. Rather than utilizing a preformed groove, the Rieber process provided a prestressed and anchored elastomeric gasket during the belling operation. The Reiber gasket has a homogeneous gasket body bonded to an internal or external metal wire or band, the band preventing rubber deformation, thus allowing a heated and softened pipe end to be pushed over the gasket. Because the gasket was installed simultaneously with the formation of the belled pipe end, a rigid, embedded reinforcing ring could be supplied as a part of the gasket. Because the pipe groove or raceway was, in a sense, “belled over” and formed around the gasket with its embedded reinforcing ring, the gasket was securely retained in position and did not tend to twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
Despite the advances offered by the Rieber process, there were some situations in which the “belled over” gasket design could be a disadvantage. For example, certain situations exist in which it would be desirable to manually remove one gasket and reinstall another within a preformed raceway in the selected pipe end, rather than utilizing an integrally installed gasket in which the groove in the pipe is formed around the gasket. For example, municipal and consulting engineers will specify specialty elastomers based on the pipelines end-use and soil conditions. While SBR is the most common rubber used in North America, engineers will specify EPDM based on water treatment technique, and nitrile rubber when there is hydrocarbon soil contamination due to gasoline or oil pollution. Distributors and contractors cannot exchange Rieber process gaskets in their pipe inventory.
The prior art Rieber manufacturing process necessarily requires a pipe company to hold inventory to make a production run of gasketed pipe. Without prior art Rieber gaskets on-hand, pipe cannot be produced. It would be advantageous to be able to place a specially designed gasket on a belling mandrel, use the gasket as a raceway forming device, form a bell and raceway, and then remove the gasket from inside the bell. The gasket could then be placed on the belling mandrel again to form an additional pipe. Pipe could be produced and sent into inventory and gaskets installed into the bell raceways at a later date.
The gaskets used in the prior art Rieber process were typically injection molded with a wire or band embedded in the rubber to hold the gasket dimensions and make subsequent Rieber belling process possible. The steel wire, or band, must be treated to assure rubber-to-metal bonding, and coated to inhibit oxidation and corrosion. The wire or band was held in place with small pins. As gaskets are designed having very small cross sections, a wire is used, and the wire itself is very small in cross section. It becomes difficult to hold the wire in position and the small pins become susceptible to damage. It would thus be of an advantage to be able to use a specially designed gasket which would not require the use of pins in the gasket molding process. The elimination of the mold pins reduces mold maintenance cost and allows for production of Rieber belled pipe of reduced cross sections not previously possible.
It would therefore be advantageous to be able to install a gasket of the type having a reinforcing element within a previously belled pipe end, as opposed to those systems like the Rieber systems, where the female pipe end is formed about the sealing gasket during the manufacture of the female pipe end. However, prior art gaskets with reinforcing elements are subject to breakage and are not easily bent or flexed by hand, thus generally precluding hand assembly in the field.
It would also be advantageous to provide a gasket and manufacturing process that would use the Rieber “belled over” gasket manufacturing process, but which would also allow the gasket to be removed by hand if desired. Many pipe companies exclusively utilize the “belied over” Rieber process, eliminating their ability to sell pipe having “exchangeable gaskets.”
U.S. Pat. No. 6,044,539, issued Apr. 4, 2000, to Guzowski, and commonly owned by the present applicant describes a machine for inserting a “snap-fit” gasket, unable to accept inverse curvature, having an embedded reinforcing ring into a preformed gasket receiving groove in a belled pipe end. However, such a machine was fairly costly to construct and presented difficulties in being hand carried by a worker in the field. Once installed this gasket is very difficult to remove without damage to the embedded ring.
The present invention has, as one object, to provide an improved pipe gasket for use in pipe joints which offers the advantage of the “belled over” Rieber process, while allowing the gasket to accept inverse curvature, to be installed in a preformed groove by hand, either at the manufacturing plant or in a field operation.
An alternative object of the invention is to provide a gasket for use in pipe joints which offers the advantage of the Rieber style manufacturing process and yet which can be removed by hand, if desired.
Another object of the invention is to provide an improved gasket which is securely retained within a preformed pipe groove without the necessity of a treated, coated and bonded metal retaining band.
Another object of the invention is to provide an improved sealing gasket of the plastic/rubber variety which optimizes the rubber sealing surface contact of the gasket with the pipe bell raceway.
Another object of the invention is to provide a reinforcing element that is not required to be bonded to the rubber element, hence creating the possibility of being made from a multitude of plastic materials.
Another object of the invention is to extend the “belled over” Rieber process to a small diameter, and small gasket cross sections than currently possible.
Another object of the invention is to provide such a sealing gasket with special reinforcing attributes which allow it to seal under a variety of pressure conditions without being twisted or extruded, or displaced during field assembly.